Application Ser. No. 07/985,406 filed of even date herewith and assigned to the same assignee as the instant invention and this application relate to the same subject matter.
This invention relates generally to a solid state circuit controller and more specifically to a solid state circuit controller for switching power to a load and for protecting the switch from damage due to power dissipation.
In copending application, Ser. No. 07/985,406, assigned to the assignee of the present invention, a solid state circuit controller is described and claimed which has utility in many applications, such as, by way of example, in aircraft power distribution systems.
In the controller described in that application an analog voltage is produced proportional to a wire or load temperature rise or energy equation which produces a trip signal when the maximum temperature rise of the wire, simulated by a reference voltage, is reached. The section comprises a linear circuit which measures the current flow through the wire, calculates its heating impact on the wire and provides a signal to trip the controller when the wire temperature has risen its maximum safe level as defined by a selected curve set such as one derived from the MS3320 trip time vs load current curves. The circuit reads the current in the wire as a voltage signal across a shunt resistor serially connected to the wire, a signal is scaled by an amplifier stage, squared with the resultant applied to an RC network. The output voltage from the RC network is monitored by a comparator which has a threshold set by the referenced voltage according to an energy equation. When the output voltage of the RC network reaches the threshold level the comparator output transitions to an opposite state signaling the Logic section of a trip condition in order to interrupt current flow within the wire by turning off solid state switch means connected to the wire, e.g., one or more MOSFETs.
It is an object of the present invention to provide protection of such MOSFETs from thermal damage due to power dissipation. Another object is the provision of controller apparatus for supplying a selected level of current to a load. Yet another object is to provide apparatus to protect solid state power switches used both to limit current flow therethrough, and to switch high voltage DC, from thermal damage from power dissipated in the switches.
Various other objects and advantages will appear from the following description of an embodiment of the invention and the novel features will be particularly pointed out hereinafter in connection with the accompanying drawings and the appended claims.